1. Field of the Invention
The present invention relates to a motor driving apparatus for driving and braking a brake-equipped motor used in a machine tool, an industrial machine, a robot, or the like.
2. Description of the Related Art
Motor driving apparatus for driving and braking a brake-equipped motor used in a machine tool, an industrial machine, a robot, or the like include the type that has a DC power supply which is used both as a motor driving power supply and as a brake driving power supply.
Patent Document 1 discloses a brake control method for a robot in which, to prevent, for example, a robot arm from falling in the event of an emergency stop or power interruption, a brake is provided within a motor or on a rotating shaft that moves the robot arm, with provisions made to actuate the brake by de-energizing the brake coil upon occurrence of an emergency stop or power interruption.
FIG. 1 is a block diagram showing the configuration of a motor driving apparatus according to the prior art. Motor driving apparatus 101 is an apparatus for driving a motor 102 and for actuating a brake 103, and includes a control unit 110 and a driving unit 120. Control unit 110 supplies a speed command for motor 102 and a brake application command or brake release command for brake 103 to driving unit 120. Brake 103 is a power-off brake, and motor 102 can be braked by de-energizing the coil of brake 103. Driving unit 120 includes a motor/brake driving DC power supply 121 which is used both as a motor driving power supply and as a brake driving power supply, a motor driving circuit 122 which receives a speed command for motor 102 from control unit 110 and drives motor 102 at the commanded speed, and a brake driving circuit 123 which receives a brake application command or brake release command for brake 103 from control unit 110 and applies or releases brake 103 in accordance with the received command.
Patent Document 2 discloses an electromagnetic brake control apparatus which, when drawing a moving plate in an electromagnetic braking device by attraction (forceful energization state), performs control so that a large current is flown only during the drawing stroke that lasts briefly, and thereafter, the current flowing to the electromagnet of the electromagnetic brake is held at a relatively small level just sufficient to hold the moving plate in the attracted position (sustained energization state) by accurately controlling the energization current to the electromagnet at all times independently of the operating condition of the electromagnetic brake, that is, by properly controlling the energization current to the electromagnet of the electromagnetic brake so as to ensure high reliability and stable braking action while achieving sufficient energy saving. This electromagnetic brake control apparatus employs a method that controls the energization current to the electromagnetic brake actuating electromagnet through phase control by a thyristor from a commercial AC power supply, and detects the energization current supplied to the electromagnet of the electromagnetic brake and controls the firing angle of the thyristor in accordance with the deviation of the detected value from a reference value.
[Patent Document 1] Japanese Unexamined Patent Publication No. H07-328966 (see [CLAIM 1] of the claims, paragraph numbers [0002], [0007], [0011], and [0012] of the specification, and [FIG. 1] of the drawings) and Abstract of the Disclosure.
[Patent Document 2] Japanese Unexamined Patent Publication No. H06-200963 (see [CLAIM 1] of the claims, paragraph numbers [0002] to [0012], [0015] to [0017], [0051], and [0052] of the specification, and [FIG. 1] of the drawings) and Abstract of the Disclosure.
In the brake control method for a robot disclosed in Patent Document 1, the motor/brake driving DC power supply is used for driving the brake as well as for driving the motor, but in this case, because of the fluctuation in supply voltage during the driving of the motor, in particular, the fluctuation in supply voltage associated with the acceleration and deceleration of the motor, the voltage applied to the brake coil as the brake driving power becomes unstable, and in the worst case, the brake coil may be damaged.
In the electromagnetic brake control apparatus disclosed in Patent Document 2, while improvements can be achieved in terms of the stability of braking action and the reduction of energy consumption, reducing the time required to release the brake or effect the braking is not considered.